Which of the following is wrong?

Options

A. Cathode rays have constant e/m ratio
B. e/m ratio of anode rays is not constant
C. e/m ratio of protons is not constant
D. e/m ratio of `beta`-particles is constant.

Explanation

To determine which of the given statements is wrong, we will analyze each statement regarding the e/m (charge-to-mass) ratio of different particles.

### Step-by-Step Solution:

1. **Statement Analysis: Cathode Rays have a constant e/m ratio.**
- Cathode rays are streams of electrons. Since all electrons have the same charge and mass, the e/m ratio (charge-to-mass ratio) for cathode rays is indeed constant.
- **Conclusion:** This statement is **correct**.

2. **Statement Analysis: The e/m ratio of anode rays is not constant.**
- Anode rays consist of positive ions, which can vary in mass and charge depending on the type of gas used in the discharge tube. Different ions will have different e/m ratios.
- **Conclusion:** This statement is **correct**.

3. **Statement Analysis: The e/m ratio of protons is not constant.**
- Protons are positively charged particles with a fixed mass. Since all protons have the same charge and mass, their e/m ratio is constant.
- **Conclusion:** This statement is **wrong**.

4. **Statement Analysis: The e/m ratio of beta particles is constant.**
- Beta particles are essentially electrons (or positrons in the case of beta plus decay). Since electrons have a constant mass and charge, their e/m ratio is also constant.
- **Conclusion:** This statement is **correct**.

### Final Conclusion:
The statement that is wrong is: **The e/m ratio of protons is not constant.**